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Biomedical subjects

P Williamson

Publications and source records attributed to P Williamson.

At least 19 recordsLinked to original sources
PubMed1992

Dyskeratosis congenita fibroblasts are abnormal and have unbalanced chromosomal rearrangements.

Dyskeratosis congenita (DC) is a rare inherited disorder characterized by bone marrow failure, dystrophic changes in the skin and mucous membranes, and a predisposition to malignancy. The DC locus has been mapped to Xq28. The primary defect responsible for this disease remains unknown. We have studied four patients with this disease, three from one family and one from another. In all four patients, primary skin fibroblast cultures were abnormal both in morphology (polygonal cell shape, ballooning, and dendritic-like projections) and in growth rate (doubling time about twice normal). Fibroblast survival studies using four clastogens (bleomycin, diepoxybutane, mitomycin-c, and 4-nitroquinoline-1-oxide) and gamma radiation showed no significant difference between DC and normal fibroblasts. Cytogenetic studies performed on peripheral blood lymphocytes showed no difference between DC and normal lymphocytes with or without prior incubation with clastogens. However, bone marrow metaphases from one of three patients and fibroblasts from two of four patients (who were the eldest of the 4) showed numerous unbalanced chromosomal rearrangements (dicentrics, tricentrics, and translocations) in the absence of any clastogenic agents. Cell-specific differences and a higher rate of chromosomal rearrangements in the older patients appear to correlate with the clinical evolution of the disease. These findings suggest that the DC defect predisposes DC cells to developing chromosomal rearrangements.

Adolescent↗
PubMed1992

Ca2+ induces transbilayer redistribution of all major phospholipids in human erythrocytes.

Elevating cytoplasmic Ca2+ levels in erythrocytes activates a pathway for transbilayer diffusion of plasma membrane phospholipids. The use of spin-labeled and fluorescent phospholipid analogues revealed that the pathway permits diffusion of all the major classes of phospholipids and does not distinguish between the two types of probes. Diffusion was bidirectional, began immediately upon elevation of cytoplasmic [Ca2+] above 50-100 microM, persisted as long as the [Ca2+] remained elevated, and disappeared promptly when Ca2+ levels fell. Diffusion was unaffected by conditions which suppress shedding of vesicles, discounting this event as a requisite for phospholipid reorientation induced by Ca2+.

Calcium↗
PubMed1992

Rapid loss and restoration of lipid asymmetry by different pathways in resealed erythrocyte ghosts.

The normal asymmetric distribution of phospholipids across the plasma membrane of erythrocytes can be abolished by lysing and resealing cells in the presence of Ca2+. In the present study, using flow cytometric analysis of the binding of merocyanine 540 to monitor transbilayer phospholipid distribution, Ca(2+)-induced loss of asymmetry is shown to be independent from the aminophospholipid translocase which catalyzes movement of normally internal phospholipids from the outer to the inner leaflet of the membrane. Loss of asymmetry is rapid, temperature-sensitive, and occurs in an uninterrupted, intact bilayer, rather than by diffusion of lipids through the hemolytic pore. Addition of ATP during lysis reverses loss of asymmetry, and this restoration can be blocked by inhibitors of the aminophospholipid translocase. These results suggest that the ATP-dependent translocase is essential for recovery of asymmetry, in turn suggesting that separate mechanisms mediate the loss and the recovery of lipid asymmetry in erythrocytes.

Adenosine Triphosphate↗
PubMed1992

Ca2+ accumulation and loss by aberrant endocytic vesicles in sickle erythrocytes.

Sickle cells contain internal vesicles which accumulate Ca2+. As shown here, the membrane enclosing the vesicles contains the plasma membrane Ca(2+)-ATPase, or Ca2+ pump, as judged by staining with an antibody directed against the protein. Moreover, the number of cells containing such vesicles increases upon deoxygenation. These findings argue strongly that the vesicles arise by endocytosis from the plasma membrane, and explain how they accumulate Ca2+. When sickle cells are depleted of ATP, Ca2+ is lost from the vesicles, as judged by the disappearance of staining with the Ca2+/membrane probe chlortetracycline (CTC), without a corresponding loss of antibody staining. This loss of Ca2+ can be inhibited by nitrendipine, a Ca2+ channel blocker. These results suggest that the vesicle membrane allows outward passage of Ca2+ by a nitrendipine-sensitive pathway, which can be overcome by the inward-directed activity of the Ca2+ pump of the vesicle membrane. If so, the Ca2+ which vesicles contain is in dynamic equilibrium with the cytoplasm of the sickle erythrocyte.

Anemia, Sickle Cell↗
PubMed1992

Single cell analysis of factors increasing the survival of resealed erythrocytes in the circulation of mice.

Erythrocytes labeled with fluorescent membrane markers were reinfused into mice. Blood samples removed periodically were analyzed by flow cytometry for survival of labeled cells. Normal erythrocytes labeled with the markers persisted in the circulation for 45 days. A fraction of lysed and resealed erythrocytes labeled with marker were rapidly cleared from the circulation; the remainder were removed at approximately the same rate as normal cells in the same animal labeled with marker of another color. Lysis in a minimal volume of buffer and addition of ATP during lysis both increased the fraction of cells surviving initial clearance.

Adenosine Triphosphate↗
PubMed1992

Binding of perforin to membranes is sensitive to lipid spacing and not headgroup.

When triggered, cytolytic effector cells (cytolytic T-lymphocytes (CTL) and large granular lymphocytes (LGL)) release effector molecules from cytoplasmic granules, including the lytic protein perforin. This protein binds and incorporates into the plasma membrane of target cells, where it aggregates to form pores which cause target cell lysis and death. Phosphorylcholine, the headgroup of the ubiquitous phospholipids phosphatidylcholine (PC) and sphingomyelin, has been proposed as the specific receptor for perforin. We report here that any headgroup specificity is outweighed by phospholipid spacing in determining binding of perforin to liposomes. We also find that the spacing of outer leaflet lipids in a natural bilayer, the plasma membrane of the erythrocyte, influences susceptibility of the cell to perforin-mediated lysis. Finally, we demonstrate that the plasma membrane lipids in CTL are more closely spaced than in target cells, suggesting that lipid spacing contributes to the relative resistance of CTL to perforin-mediated lysis.

Animals↗
PubMed1992

Frontal, temporal, and striatal proton relaxation times in schizophrenic patients and normal comparison subjects.

Spin-lattice (T1) and spin-spin (T2) magnetic resonance relaxation times were examined in frontal, temporal, and striatal regions of 24 patients with schizophrenia and 10 normal comparison subjects. The schizophrenic patients had more prolonged T2 values than did the comparison subjects, particularly in the left temporal cortex and white matter, suggesting tissue pathology.

Adult↗
PubMed1992

REM latency in endogenously depressed adolescents.

Twenty-three adolescents with DSM-III major depressive disorder (endogenous subtype) and 23 normal controls were studied polysomnographically (PSG). The depressed group showed significantly shortened REM latencies (P = 0.005) and longer sleep latencies (P = 0.04). No other PSG measures differentiated the two groups. The implications of these findings for adolescent depression are discussed.

Adolescent↗
PubMed1991

A quantitative model suggests immune memory involves the colocalization of B and Th cells.

A prominent and essential feature of the humoral immune response of vertebrates is immunologic memory: the ability to recall previous exposure to antigen. We present a mathematical model of the growth and interactions of the major cell populations involved in the humoral immune response. Our analysis of this model predicts that the formation of a dynamic association between small numbers of antigen-specific B and Th cells, "colocalization", is sufficient to account for memory and the kinetics of the secondary response--neither specifically differentiated Th or B memory cells nor networks of antigen and anti-idiotypes are required. The colocalization hypothesis explains a number of existing experimental observations and can be tested by straightforward experiments which we describe.

Animals↗
PubMed1991

Bilayer/cytoskeleton interactions in lipid-symmetric erythrocytes assessed by a photoactivable phospholipid analogue.

Two mechanisms have been proposed for maintenance of transbilayer phospholipid asymmetry in the erythrocyte plasma membrane, one involving specific interactions between the aminophospholipids of the inner leaflet of the bilayer and the cytoskeleton, particularly spectrin, and the other involving the aminophospholipid translocase. If the former mechanism is correct, then erythrocytes which have lost their asymmetric distribution of phospholipids should display altered bilayer/cytoskeleton interactions. To test this possibility, normal erythrocytes, erythrocytes from patients with chronic myelogenous leukemia or sickle disease, and lipid-symmetric and -asymmetric erythrocyte ghosts were labeled with the radioactive photoactivable analogue of phosphatidylethanolamine, 2-(2-azido-4-nitrobenzoyl)-1-acyl-sn-glycero-3-phospho[14C]ethanolamine ([14C]AzPE), previously shown to label cytoskeletal proteins from the bilayer. The labeling pattern of cytoskeletal proteins in pathologic erythrocytes and lipid-asymmetric erythrocyte ghosts was indistinguishable from normal erythrocytes, indicating that the probe detects no differences in bilayer/cytoskeleton interactions in these cells. In contrast, in lipid-symmetric erythrocyte ghosts, labeling of bands 4.1 and 4.2 and actin, and to a lesser extent ankyrin, by [14C]AzPE was considerably reduced. Significantly, however, labeling of spectrin was unaltered in the lipid-symmetric ghosts, suggesting that its relationship with the bilayer is normal in these lipid-symmetric cells. These results do not support a model in which spectrin is involved in the maintenance of an asymmetric distribution of phospholipids in erythrocytes.

Affinity Labels↗
PubMed1991

Altered erythrocyte protein kinase C activity and membrane protein phosphorylation in chronic myelogenous leukemia.

The membrane protein kinase C (PKC) content was found to be higher in erythrocytes form patients suffering from chronic myelogenous leukemia (CML) compared to normal erythrocytes. PKC activity was also higher in the cytosol and after translocation to the membrane, as assessed by histone phosphorylation. The increased PKC activity in CML erythrocytes was associated with abnormal phosphorylation of protein 4.1. Since phosphorylation-dephosphorylation mechanisms are likely candidates for controlling membrane protein associations, the altered PKC activity may be one of the factors responsible for altered thermal sensitivity and mechanical stability of CML erythrocytes.

Cytoskeletal Proteins↗
PubMed1991

Presence of human immunodeficiency virus DNA in laser smoke.

Concentrated tissue culture pellets infected with human immunodeficiency virus (HIV) containing 1 x 10(7) cells/ml were vaporized by means of a carbon dioxide laser. The vaporous debris resulting from the laser's impact were evacuated through sterile silastic tubing, then bubbled through sterile culture medium (RPMI) positioned in series with a commercial smoke evacuator. No HIV DNA was detected in the culture medium flask. Tissue culture studies of the silastic collection tubing revealed p24 HIV gag antigen in 3 of 12 tube segments at the end of 1 week and in 1 of 12 tube segments at 2 weeks. No sustained infection of HIV cultured cells was observed at the 28th day. Polymerase chain reaction (PCR) analysis of particulate debris obtained from the silastic collection tubing was positive from proviral HIV DNA in both immediately sampled and day 14 cultured material.

Culture Techniques↗
PubMed1991

The gonadotropin-releasing hormone (Gnrh) gene maps to mouse chromosome 14 and identifies a homologous region on human chromosome 8.

The murine gonadotropin-releasing hormone (Gnrh) locus has been mapped to mouse chromosome 14 using a mouse x Chinese hamster somatic cell hybrid panel. The equivalent human locus, known as luteinizing hormone-releasing hormone (LHRH), has been previously mapped to 8p21-8p11.2. Four other loci mapping to the human chromosome 8 short arm have been mapped to mouse chromosome 8; two of these (PLAT, GSR) lie proximal to LHRH, and two (LPL, DEF1) lie distal to LHRH. The localization of Gnrh, the murine homolog of LHRH, to mouse chromosome 14 therefore defines a hitherto unrecognized block of homology between man and mouse. Furthermore, it indicates that the region of homology between the human chromosome 8 short arm and mouse chromosome 8 is composed of two separate blocks.

Animals↗
PubMed1991

Prognostic factors for overall survival in patients with advanced ovarian carcinoma.

Twenty-one pretreatment variables were investigated for prognostic influence on survival in 301 previously untreated patients with ovarian carcinoma, stage IIB-IV. Patients were randomized to sequential combination chemotherapy: cyclophosphamide, doxorubicin, 5-fluorouracil, followed by cisplatin and hexamethylmelamine, or to the 3-drug combination alternating with the 2-drug combination every other month. Median overall survivals were 25 and 22 months, respectively, P greater than 0.4. Based on the results from a Cox multivariate stepwise analysis a subset of independent significant prognostic factors was found to include: residual tumor size, performance status, alkaline phosphatase, number of metastases, histological differentiation grade and type. A prognostic index was calculated for each patient and three prognostic categories of patients were determined. The 3-yr survival rates for patients with low-, intermediate-, and high-risk scores were 62, 31, and 7%, respectively. Multivariate analysis thus contributes further information about the disease, and a knowledge of the distribution of such factors across different trials is important when comparing treatment outcome.

Antineoplastic Combined Chemotherapy Protocols↗